Describe the structure of an HTTP request and response. How are response codes classified?

An HTTP request consists of several parts:

1. Request line: contains the method (GET, POST, etc.), URI, and protocol version. Example: GET /index.html HTTP/1.1
2. Headers: key-value pairs that convey meta-information (e.g., Host, User-Agent, Content-Type).
3. Body: optional, contains data (e.g., in POST requests).

An HTTP response also consists of:

1. Status line: protocol version, status code, and status message. Example: HTTP/1.1 200 OK
2. Headers: meta-information about the response (e.g., Content-Type, Content-Length).
3. Body: content (HTML, JSON, file, etc.).

Response codes are classified by their first digit:

• 1xx (Informational): request received, processing continues.
• 2xx (Success): request successfully processed (e.g., 200 OK, 201 Created).
• 3xx (Redirection): additional action required from the client (e.g., 301 Moved Permanently).
• 4xx (Client errors): error on the client side (e.g., 404 Not Found, 400 Bad Request).
• 5xx (Server errors): error on the server side (e.g., 500 Internal Server Error).

Example of a request and response in Go:

req, _ := http.NewRequest("GET", "https://example.com", nil)
client := &http.Client{}
resp, err := client.Do(req)
if err != nil {
    log.Fatal(err)
}
defer resp.Body.Close()
fmt.Println("Status code:", resp.StatusCode)

This is the basic structure and classification of HTTP messages.